Signalling system for automatic fire alarm installation



12, 1958 E. G. LINDGREN 2,8

SIGNALLING SYSTEM FOR AUTOMATIC FIRE ALARM INSTALLATION Filed March 25,1955 f/VVEA/FOR ER/K Cusrwr A /NDGREA/ HM WNW firromvs rs United StatesPatent SIGNALLING SYSTEM FOR AUTOMATIC FIRE ALARM INSTALLATION ErikGustaf Lindgren, Stockholm, Sweden, assiguor to Telefonaktiebolaget L MEricsson, Stockholm, Sweden, a corporation of Sweden Application March25, 1955, Serial No. 496,880

Claims priority, application Sweden April 1, 1954 7 Claims. (Cl.340-227) The present invention relates to a signalling system for anautomatic fire alarm installation. There are known signalling systemsfor fire alarm installations in which one or more two-wire circuitsystems are continuously kept under current and normally opentemperature responsive alarm switches bridge the two wires of thecircuit systems. These alarm switches close their contacts in responseto an excessive temperature caused by fire, thereby short-circuiting thetwo wires whereby an energizing circuit is closed for an alarm device.

One of the objects of the present invention is to provide a signallingsystem for fire alarm installations of the general kind above referredto, which discriminates between changes in the circuit system caused bya line fault and changes caused by closing of an alarm switch due tofire and which indicate the cause of the change in the circuit bydifferent signals. Such arrangement affords the advantage of eliminatingthe annoyance of a false fire alarm.

Another object of the invention is a signalling system the signals ofwhich indicate the approximate location of the fire thereby expeditingthe required steps for extinguishing the fire.

Still another object of the invention is to provide a signalling systemin which the total area to be supervised is divided in sectional areaseach of which is individually supervised by the associated detecting andindicating means whereby the approximate location of a fire or anothercause causing an excessive temperature can be more readily located.

Other and further objects, features and advantages of the invention willbe pointed out hereinafter and set forth in the appended claims formingpart of the application.

In the accompanying drawing, several preferred embodiments of theinvention are shown by way of illustration and not by way of limitation.

In the drawing:

Fig. 1 is a diagrammatic circuit system of the entire installationaccording to the invention,

Fig. 2 shows a network modifying the detecting means of theinstallation, and

Fig. 3 shows another modification of the detecting network.

Referring now to the figures more in detail, the signalling system andinstallation according to the invention comprises a two-wire circuitsystem, the two wires or branches of which are designated by a and b,and a central control installation including four relays 1, 11, 12, 13and four signalling lamps 14, 15, 16 and 17. Relay 1 is a common controlrelay controlling contact arms 20, 8, 9, and 21. Relay 1 is shownenergized and it is assumed that in accordance with the conventions usedfor the diagrammatic showing of relays and the contact arms thereof, thecontact arms move into the direction away from the relay coil when therelay deenergizes, that is, contact arm 20 will move to the left and theother contact arms to the right. As is evident, the contact 2,847,662Patented Aug. 12, 1958 "ice arms of relay 1 and the contacts 2, 3, 4 and5 controlled thereby divide the total area supervised by wires a and 11into three sections, but of course a greater number of sections may beprovided such as five to ten sections. Relays 11, 12 and 13 constitutesupervisory or indicating relays, each being assigned to one section.Each section further encloses an alarm or detecting switch 7. Theseswitches are connected across wires a and b and are parallel with eachother. The switch contacts of switch 7 are normally open, but close inresponse to an excessive temperature caused, for instance, by a fire,thereby directly short-circuiting wires a and 12. Temperature responsiveswitches of this kind are well known in the art and any suitableconventional type may be used.

The indicating means of the installation comprise a lamp 14 controlledby a relay 1 and lamps 15, 16 and 17 controlled by relays 11, 12 and 13respectively.

To simplify the illustration, only one circuit system is shown butobviously several may be provided. In such arrangement each installationhas its own control relay 1 but the indicating relays 11, 12 and 13 maybe common to several circuit systems a and b, in which event they areconnected to the several systems as shown for one system.

The operation of the arrangement is as follows:

A direct current circuit is normally closed from the positive pole of asource of current through branch a, the coil of relay 1, branch bincluding relay contacts 2, 3, 4 and 5 connected in series and aresistance 6 to the negative pole. If there is a break in line branchesa and b or a short-circuit between them, the flow of current through thecoil of relay 1 is interrupted or at least decreased. As a result therelay releases and its contacts 2, 3, 4 and 5 are opened due to themovement of contact arms 8, 9, 10 and 21 to the right. Branch b is nowdivided into three sections each of which is connected through contactarms 8, 9 and 10 to supervisory relays 11, 12 and 13. As is evident, therelease of control relay 1 due to a break in the circuit will not closean energizing circuit for any of the supervisory relays as the circuitof each of the relay coils includes one of the alarm switches 7 whichare still open. However, signalling lamp 14 is closed due to a movementof contact arm 20 to the left as previously described. Ignition of lamp14 indicates that there is a fault in the circuit.

Let it now be assumed that there is a fire within the area supervised bythe installation. Then one or several of the temperature responsivealarm switches '7 will close thus short-circuiting lines a and b andclosing an energizing circuit for the respective supervisory relay 11,12 or 13. If for instance relay 12 is energized in a circuit from thepositive pole through the a branch, the respective alarm switch 7, relaycontact arm 9 and the coil of relay 12 to the negative pole, the relaywill attract its contact arm 22 thereby closing a circuit for signallamp 16.

As is apparent, in the circuit system according to Fig. 1 any directshort-circuit between the line branches at and [2 due to causes otherthan fire, but electrically equivalent to a closing of a switch 7, willset off a false fire alarm signal. Experience shows that faults of thisnature are extremely rare and in any event occur much less than faultscaused by a break in the circuit and resulting merely in a lighting ofsignal lamp 14.

In a further development of the invention, Figs. 2 and 3 show networkswhich eliminate the aforementioned rare but possible source of falsealarm.

According to Fig. 2 a current direction dependent impedance means 18shown as a rectifier is connected in series with each of the alarmswitches 7. If new the supervisory relays 11, 12, and 13 are connectedto a source of current producing a polarity shifting direct current oran alternating current, release of control relay 1 due to deenergizationby the closing of an alarm switch 7 willpermit fiow of'current in onedirection only through the closed alarm switch and the respectivesupervisory relay. However, when current is supplied due to a directshort-circuit between theline branches a flow of current in-bothdirections will reach the respective supervisory relays. Thesupervisoryrelays used in this arrangement are of the well-known kindwhich does not respond to current flowing in both directions, but tounidirectional current only. Consequently a direct short-circuit causedby a'fault rather than by a fire effecting closing of an alarm switchwill be correctly indicated as a line fault by the closing of circuit oflamp 14 by relay 1.

According to Fig. 3 a voltage dependent resistance19 is connected inseries with each of the alarm switches 7. Such resistance, for instancea siliceous carbide resistance, decreases its resistance value as thevoltage across the resistance increases. A source of current suppliesthe supervisory circuit including relays 11, '12 and 13 with current ofvarying voltages, namely a normal voltage and a voltage higher thannormal. If the current strengths, which in the event of a short-circuitreach a supervisory relay, are proportional to the voltages that occurthrough a short-circuit due to a line fault; the respective supervisoryrelay cannot respond due to its arrangement. However, when the relationbetween the current strengths is greater than the relation between thevoltages which occur when alarm switch 7 is closed, the respectivesupervisory relay responds and closes the circuit of its signal lamp 15,16 or 17.

As is evident the arrangements of Figs. 2 and 3 both prevent a falsefire alarm signal due to a line fault.

What is claimed is:

l. A signalling system for an automatic fire alarm installation, saidsystem comprising, in combination, a closed two-wire energizing circuitmeans, a plurality of cross connections across the two wires eachincluding a detecting temperature sensitive switch contact biased intothe open position but closing in response to an ambient temperatureabove a predetermined value, a common control relay means having andcontrolling a plurality of pairs of relay contacts, the coil of saidrelay means and one contact of each pair being included in series insaid two-wire circuit means, the said series contacts being closed inthe energized state of said relay 0nd contact of a respective pair, anda plurality of indicating means each controlled by a respective one ofsaid supervisory relay means whereby, upon deenergization of saidcontrol relay means only due to a fault in said twowire circuit means,said circuit means is separated in a plurality of networks by opening ofsaid series contacts, each network including a respective supervisoryrelay means and at least one open detecting contact and whereby, upon.closing of one of said detecting contacts and deenergization of saidcontrol relay means due to an excessive ambient temperature, saidtwo-wire circuit means are separated in said several networks and therespective supervisory relay means is energized for actuating its signalmeans over said other contact of the respective pair of relay contacts.

2. A system according to claim 1, wherein said common control relaymeans controls an indicating means, said indicating means being actuatedupon deenergization of said control relay means.

3. A system according to claim 1, wherein a unidirectional impedancemeans is included in each of said connections across the wires of saidcircuit means, each of said supervisory relay means being arranged to beactuated in response to a flow of current ina predetermined directiononly due to the closing of the respective detecting contact.

4. A system according to claim 3, wherein said impedance means comprisesa rectifying means.

5. A system according to claim 1, wherein said twowire circuit means areenergized with different voltages, and wherein each of said crossconnections includes a voltage responsive impedance means, saidsupervisory relay means being arranged to be actuated only in responseto a current strength caused by a voltage due to a closing of adetecting contact.

6. A system according to claim 5, wherein said impedance means comprisesa resistance means having a characteristic decreasing the resistancevalue thereof in response to an increasing voltage.

7. A system according to claim 6, wherein said resistance meanscomprises a siliceous carbide resistor.

References Cited in the file of this patent UNITED STATES PATENTS1,537,211 Wooton May 12, 1925 2,605,342 Spurling July 29, 1952 2,695,994Lode Nov. 20, 1954

